The present invention generally relates to stent devices for delivery on foldable delivery balloons and, more particularly, to a stent configured for mounting on a balloon in a releasable gripping relationship.
Angioplasty is a procedure in which a balloon is positioned in an artery at the site of a lesion and expanded to compress the materials at the lesion in order to open the restricted area in the artery. In this procedure, a balloon is formed on one end of a catheter. The catheter is inserted transluminally over a previously placed guide wire to maneuver the balloon through the patient""s vessels to the site of the lesion. When the uninflated balloon is properly positioned at the lesion, the balloon is inflated to dilate the restricted area.
In these procedures there may be restenosis, also referred to as recurrent stenosis, of the artery. Restenosis may require another angioplasty procedure, a surgical bypass operation, or some method of repairing or strengthening the area. To reduce the risk of restenosis and strengthen the area, a physician can implant at the treatment area an intravascular prosthesis for maintaining vascular patency, typically called a stent. A stent is a device used to hold tissue in place or to provide support for a graft or tissue joined while healing is taking place. Stents are typically implanted by use of a delivery catheter which is inserted at an easily accessible location and then advanced through the vasculature to the deployment site. The stent is initially maintained in a radially compressed or collapsed state to enable it to be maneuvered through a body lumen. Once in position, the stent is usually deployed either automatically by the removal of a restraint, or actively by the inflation of a balloon about which the stent is carried on the delivery catheter. In reference to balloon catheter stents, a variety of devices are known in the art for use as stents, including coiled wires and wire mesh sleeves in a variety of patterns that are able to be crimped onto a balloon catheter, and that are capable of retaining their expanded form. Typically, the stent is mounted and crimped onto the balloon portion of the catheter, and advanced to a location inside the lumen at the lesion. The balloon is then inflated to expand the stent to a larger diameter to permanently implant it in the artery at the lesion.
As previously mentioned, an attribute of a stent delivery system is its ability to have the stent tightly crimp on the balloon portion during stent delivery. This form of mechanical interlock between the stent and catheter balloon is known as stent security. The objective of stent security is to prevent the stent from moving relative to the balloon during delivery of the stent in the patient""s vasculature. Good stent security is important in preventing the stent from separating from the balloon before the delivery system is in a desired anatomical location and to hold the stent in the desired position on the balloon. A stent that is repositioned on a balloon or a stent that is separated from the balloon may cause many adverse complications. One such adverse complication includes deploying the stent in a less than optimal anatomic location. This complication can lead directly to a complete occlusion of an artery. Moreover, if the stent should slide off the delivery catheter prior to expansion, the stent may somewhat block the flow of blood and could require an emergency surgical procedure to recapture the stent.
In the assembly of a stent delivery system, the balloon portion is typically folded around the catheter shaft in a xe2x80x9cjelly rollxe2x80x9d configuration. The stent is then slid over the folded balloon and squeezed down or xe2x80x9ccrimpedxe2x80x9d onto the balloon.
Current stent delivery construction poses certain shortcomings. For example, those arrangements where the balloon is pressed between the stent mesh impose design constraints on the amount of stent material that can be used and on the stent metal pattern. Other methods may result in an increase in the stent delivery system diameter or profile, which in turn increases the risk of clinical complications and can prevent the delivery of the stent to tight, distal lesions.
An improved stent with enhanced security is therefore needed to overcome the problems in the prior art. More particularly, the improved stent should provide a higher degree of safety than conventional stents and should be comparatively inexpensive to manufacture. The present invention satisfies these and other needs.
Briefly, and in general terms, the present invention provides a new and improved apparatus and method to be used in stent delivery on foldable delivery balloons. More specifically, the apparatus and accompanying method provide a stent configured for mounting on a balloon in a releasable gripping relationship which increases stent retention on the delivery catheter.
In general terms, this invention describes a novel apparatus and method to enhance stent security by incorporating balloon clips on the stent which are adapted to grip the folds which are created when the catheter balloon is initially folded. A critical attribute of a stent delivery system is stent security. In the context of this invention, stent security is achieved through the mechanical interlock between the stent and the catheter balloon. The objective of stent security is to prevent the stent from moving relative to the balloon.
In one aspect of the present invention, the stent device incorporates tethering clips which are adapted to hold the stent on the balloon portion of the delivery catheter. The stent device slides over the balloon which is folded on the delivery catheter. The tethering clips are configured so as to be positionable in a releasable gripping relationship within the folds in the folded balloon. In this configuration, the clips will be gripped by a fold in the balloon as the device is inserted into a patient""s vasculature. After the balloon is inserted into the body vessel and properly positioned in the area of treatment, it is inflated. The tethering clips are constructed so they will be released from the folds of the balloon as the balloon inflates to allow the stent to be freely deployed within the body vessel.
In another aspect of the present invention, the stent can include one or more longitudinal struts to which the tethering clips are connected. The clips are carried on their respective ends by the strut to leave a free-end shape which can be placed within the folds of the balloon during manufacture.
The free end of the clip may be in the form of a stop to create frictional resistance between itself and the balloon. This mechanical interlock between the stent and the catheter balloon thus provides increased stent security by resisting movement of the stent relative to the balloon. The stop itself can take many different configurations including a knurled surface, corrugated body, or an enlarged tip. All of these configurations should provide a suitable frictional attachment within the folds of the balloon as the stent is being inserted into a patient""s vasculature.
The tethering clips can also be coupled to, and configured on, the stent in a variety of other ways to provide the mechanical interlock between the stent and the balloon. In one aspect of the present invention, the tethering clips are pivotally mounted on the strut so as to enable the clips to be easily rotated into a position to secure the stent to the balloon.
The clips also can be formed from a ductile material. In this instance, the ductility of the clip enables it to be easily orientated for positioning into a balloon fold. After being positioned, the clip""s natural resistance to bending performs the mechanical interlock function between the balloon and the stent.
The present invention can be made with a plurality of clips connected to the stent. Each clip can be configured in either of the configurations mentioned above so as to provide a suitable mechanical interlock between the stent and the balloon.
In an accompanying method, an intra-luminal stent including at least one tethering clip is positioned in a fold of a folding delivery balloon. The tethering clips are positioned in the folds so as to releasably hold the stent in position mechanically locked on the balloon. After the stent and balloon are mechanically interlocked, the catheter system is inserted into a patient""s vasculature to deliver the stent to a desired deployment location. When the balloon is inflated, clips are released from the balloon fold and the stent continues to expand. At completion of inflation, the balloon is removed and the stent it securely implanted into the patient""s body vessel.
These and other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention.